This invention relates to a distribution breaker, having a toggle link used in an opening-closing mechanism, and more particularly to a circuit breaker in which an impact transmitted to a trip lever at the time of an on-operation is eliminated, thereby preventing a mistrip when the on-operation is effected.
Distribution circuit breaker, having a toggle link used in an opening-closing mechanism, has been extensively used, and such circuit breaker has been designed to be compact. One example is disclosed in JP-B-1-32618 entitled “WIRING BREAKER”. In this conventional circuit breaker, when a movable arm mounted on a handle is rotate from an OFF position to an ON-position, a toggle link is extended under the influence of a tension spring, extending between a common shaft, interconnecting upper and lower portions of the toggle link, and the movable arm, so that a moving contact is moved to an ON-position. Once the moving contact is moved to the ON-position, a trip lever for a disengaging operation is held in an ON-position by a retaining plate unless the trip lever moves to an OFF position manually, or the trip lever is operated by an excess current, and therefore the moving contact is held in the ON-position in a stable manner.
In the above conventional technique, an impact force, which is applied to the trip lever when the handle is rotated from an OFF position to an ON position, is alleviated using a shock-absorbing tube provided on the trip lever. However, as a result of improvement of the distribution breaker so as to meet the requirement for a more compact design and the requirement for improved excess current characteristics, it has been difficult to adequately absorb this impact force. As a result, a problem arises immediately when the operator releases the handle after the ON-operation. A trip (mistrip) typically occurs.
The inventors of the present invention have made an extensive study of the causes of this mistrip, and have found that since the trip lever is held on a fixed frame supporting the moving contact of the distribution breaker, the trip lever receives vibrations when the moving contact is pressed against a fixed contact with a large impact force by the toggle link, resulting in an occurrence of mistrip. Namely, for purposes of achieving a compact design of the distribution breaker, it is effective to suitably mount the structure for driving the moving contact in one fixed frame. In this case, however, it has been found that there arises a problem that the impact force, produced by the ON-operation, is applied to all of the constituent elements.